Sphingolipids are particularly important in these structures: a. membranes b. lipoproteins c. the brain and nervous system. d. membranes, the brain and the nervous system. e. all of these are correct

The correct option is d. Membranes, the brain and the nervous system.

Explanation:

The sphingolipids are a class of lipids which contain a sphingosine amino alcohol.

The main function of sphingolipid is the protection of the cells against harmful environment by forming a chemically resistant and mechanically stable membrane.

Sphingolipids are present in abundance in the brain and in the central nervous system where they are the important constituents of the plasma membranes. They are also important for the proper functioning, development and maintenance of the nervous system.

Therefore, Sphingolipids are particularly present in the membranes, the brain and the nervous system.

Since Titan orbits roughly along Saturn's equatorial plane, and Titan's tilt relative to the sun is about the same as Saturn's, Titan's seasons are on the same schedule as Saturn's—seasons that last more than seven Earth years, and a year that lasts 29 Earth years.